Process for the production of laminated cores

ABSTRACT

The method of manufacturing a sheet stack for electromagnetic assemblies, consisting of ferromagnetic material, includes forming the sheet stack from raw magnetic steel sheets in a shaping tool without the use of spacers, if necessary with the help of positioning aids, and simultaneously introducing a hardenable mixture into the shaping tool in order to totally surround the sheet stack and to form an anti-corrosion layer and hardening or hardening out this casting compound according to the pressure-gelating method to connect the sheets together and to form the finished sheet stack in one single working step. An electromagnetic assembly including at least one of the sheet stacks and an additional component is made in the same working step by a method including making the finished sheet stack in accordance with the foregoing pressure-gelating method, connecting the finished sheet stack to the additional component to form the assembly and surrounding the assembly with the mixture in order to form the anti-corrosion layer.

BACKGROUND OF THE INVENTION Field of the Invention

The invention relates to a method of manufacturing sheet stacks forelectromagnetic assemblies, consisting of ferromagnetic material, andfor the manufacture of electromagnetic assemblies provided with suchsheet stacks and one additional component. The invention also relates tosheet stacks and components manufactured according to these methods.

Electromagnetic assemblies which operate with alternating fields,frequently have iron cores of ferromagnetic material, which serve thepurpose of guiding magnetic fields at every point where no air gaps areprovided or desired. In order to avoid eddy current and eddy currentlosses, these iron cores are predominantly assembled from a plurality ofsheet metal blanks, which are obtained by stamping from sheet metalpanels or strips, which consist for example of steel or iron plates e.g.0.35 to 1.00 mm thick, and which are insulated from one another by alacquer coating, an oxide layer or other means. The insulation can beapplied to the bands, strips or panels either already in the rollingmill to the sheet metal band or strip, or subsequently in a specialcoating plant, and nowadays usually consists of an extremely thin silicaphosphate layer, which is applied as the sheets are rolled out.

In addition it is frequently desired to connect the individual stampedblanks together to form a solid sheet stack. This is achieved e.g. bythe use of form-fitting or positive-locking mechanical means or simplyby surrounding the finished sheet stacks or cores by a winding, in whichcase it is however also necessary electrically to insulate the windingsfrom the core.

In order to avoid such connection methods, which are in factcomparatively cost-effective, but cannot always be used, it is alreadyknown (DE 31 10 339 C2) firstly to provide strips manufactured fromsilicated magnetic steel sheet preferably on both sides with additionaladhesive layers, which consist for example of a pre-hardened duroplasticadhesive, and if necessary are applied in the rolling mill in a complex,expensive working step. The sheet stacks are then produced by stampingout sheet metal blanks or lamellae from such sheet metal strips drawnoff from coils (drums), and these are then combined into stacks andthereafter securely fastened together by heating with simultaneouspressure, in order to form a mechanically secure sheet stack. Then thefinished sheet stacks are additionally provided with a coating of anepoxy resin or the like, in order to provide the cut edges of the sheetsrevealed during cutting subsequently with an anti-corrosion layer. Thismethod is therefore in fact suitable for manufacturing compact,high-quality sheet stacks, but due to the high technical outlay and thenecessarily high manufacturing costs for coating the sheets withadhesive, is only infrequently used. A further disadvantage is that theoff-cuts occurring during stamping of the sheet metal blanks areprovided with an adhesive layer, which prevents properly categorizedrecycling of the sheet metal off-cuts, and therefore should be avoidedfor reasons of environmental protection.

Sheet stacks of the type described are in addition frequently connectedtogether with other components in order to form finished assemblies. Inthis respect it is for example known (DE 40 21 591 C2) to surround theindividual parts of the stator of an electric motor, particularly asheet stack and the associated windings, with a casting resin in ashaping tool, so that on the one hand the windings are electricallyinsulated and on the other hand a cohesive composite member is obtained.Correspondingly, it is known in manufacturing the rotors of electricmotors (DE 43 38 913 A1) firstly to assemble the associated shafts,sheet stacks, windings and commutators loosely together, and then toprovide them with a plastic covering in a shaping tool by injectionmolding, injection pressure or the like. This does in fact give rise tothe advantage that the sheet stack is subsequently provided with aninsulation or an anti-corrosion layer on the cut edges revealed duringstamping of the plates. In all these methods however a condition is thepresence of finished sheet stacks produced in the way explained above.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method formanufacturing sheet stacks and electromagnetic assemblies provided withsheet stacks, which enables the use of simple, cost-effective plates,whose off-cuts can be disposed of in an environmentally acceptablemanner, and which further requires fewer individual steps thanpreviously and therefore in particular leads to simplifications inmanufacture of the assemblies. Moreover, a high degree of mechanicalstrength and a high degree of resistance to external or internalweathering influences is to be achieved.

According to the invention the method of manufacturing a sheet stack forelectromagnetic assemblies, consisting of ferromagnetic material,comprises forming the sheet stack from raw magnetic steel sheets in ashaping tool without the use of spacers, if necessary with the help ofpositioning aids, and simultaneously introducing a hardenable mixtureinto the shaping tool in order to totally surround the sheet stack andto form an anti-corrosion layer and hardening or hardening out thiscasting compound according to the pressure-gelating method to connectthe sheets together and to form the finished sheet stack in one singlewording step.

According to the invention the method of manufacturing theelectromagnetic assembly including at least one sheet stack and oneadditional component comprises making the finished sheet stack inaccordance with the foregoing pressure-gelating method, connecting thefinished sheet stack to the additional component to form the assemblyand surrounding the assembly with the mixture in order to form theanti-corrosion layer.

Further advantageous features of the invention will become apparent fromthe sub-claims.

In a preferred embodiment of both methods according to the invention apressure of from 2 to 10 mbar is maintained in the shaping tool. Theassembly as a whole is preferably only provided with its finalelectrical, mechanical and/or geometric properties by means of thehardenable mixture and the hardenable mixture is advantageously athermally hardenable mixture.

The invention may with advantage be used at every point where sheetstacks made of ferromagnetic material are required. The term“electromagnetic assemblies” therefore in particular compriseselectrical motors on a basis of three-phase, synchronous andasynchronous current and parts thereof such for example as stators andrunners as well as choke coils with iron cores, transformers andmagnets, particularly load-raising or lifting magnets and parts thereof.

BRIEF DESCRIPTION OF THE DRAWING

The invention will be explained in more detail in the following withreference to two embodiments given by way of example, which are shown inthe accompanying drawing on slightly varying scales, in which:

FIG. 1 is a perspective, exploded view of some plates of a sheet stackfor a magnet core according to the invention;

FIG. 2 is a perspective view of the components used to produce acomplete magnet core, with the sheet stack in the stacked condition;

FIG. 3 is a perspective view of the magnet core according to FIG. 2 inthe combined condition of all the components;

FIG. 4 is a perspective view of the winding of a winding member of themagnet core according to FIG. 3;

FIG. 5 is a perspective view of a magnet pole produced with the magnetcore according to FIGS. 1 to 4, after arrangement in one half of a tool,serving to impregnate the sheet stack, for wetting through the sheetstack and the winding, for connecting the sheet stack with the othercomponents and for surrounding the entire magnet pole with a hardenablemixture;

FIG. 6 is a cross-section through the tool along the line VI—VI of FIG.5 with the magnet pole inserted;

FIG. 7 is a schematic view of the insertion of a hardenable mixture intothe tool according to FIGS. 5 and 6;

FIG. 8 is a perspective view of the completed magnet pole;

FIG. 9 is a partly exploded view of a longitudinal section through asheet stack for the stator of an electric motor;

FIG. 10 is a plan view of a section of an assembly, which comprises thesheet stack according to FIG. 9 and windings shown schematically;

FIG. 11 is a cross-section along the line XI—XI of FIG. 10;

FIG. 12 is a cross-section similar to FIG. 11 through the assembly, butafter insertion into a tool, which serves to impregnate the sheet stackand the winding, to connect the sheet stack with the windings of thestator, and to surround the entire stator with a hardenable mixture;

FIG. 13 is a schematic view of the introduction of a hardenable mixtureinto the tool according to FIG. 12; and

FIG. 14 is a cross-section similar to FIG. 11 through the finishedstator.

The invention will be explained in more detail in the following withreference to the examples of a magnet pole, which is suitable forexample for a magnetic levitation train (DE 33 03 961 C2 and DE 34 10119 A1), and of a stator for an electric motor, whose construction,function and geometry are well known to the person skilled in the artand therefore need no further detailed explanation.

In a known way, a magnet pole includes an iron core consisting of asheet stack, and a winding applied thereto. According to FIGS. 1 to 8the iron core consists of a plurality of individual sheets or lamellae1, arranged in parallel and aligned flush on one another, which havebeen obtained for example by stamping out from a ferromagnetic magneticsheet strip, which has been unwound from a drum (coil), and passed to astamping tool. According to the invention, a raw magnetic steel sheetstrip is involved. In this respect the term “raw” is understood to meanthat the magnetic steel sheet strip, contrary for example to DE 31 10339 C2, has no adhesive layer applied in a separate working procedure.On the contrary, the sheet strip, as is conventional with magnetic steelsheets, can be provided with an electrically insulating layer by meansof a lacquer coating, an oxide layer or other means which may be appliedin a cost-effective manner on both sides. This layer can already beapplied in the rolling mill to the sheet strip, and in the case ofmagnetic steel sheets conventional today usually consists of anextremely thin silica phosphate layer, which is produced as the magneticsteel sheets are rolled out. For the purposes of the invention thislayer is comparatively irrelevant, as under certain circumstances it canalso be totally omitted.

The individual sheets 1, of which only a few are shown in FIG. 1, in theembodiment have a thickness of for example 0.35 to 1.00 mm, and haveidentical dimensions, and each have a forward or rear wide side 2, andin the respective circumferential directions, a narrow upper side 3, alower side 4 and two side edges 5 and 6. In addition, they are eachprovided during the stamping procedure at identical points with at leastone hole 7 and in order to form the iron core after the stampingprocedure into packets 8 (FIG. 2), are stacked, being laid on oneanother with their forward or rear wide sides 2 flush and parallel withone another. The number of sheets 1 per packet 8 depends on the size andthickness of the magnetic pole to be produced. The mutual alignment ofthe sheets 1 is carried out appropriately with the aid of slide blocksor rods 9, upon which the sheets 1 are threaded with their holes 7. Inthe stacked sheet packet 8, for example, the upper sides 3 of theindividual sheets 1 form a magnet pole surface 10, while the undersides4 form an assembly surface 11.

After formation of the stack, the two end faces of the sheet stack 8 arerespectively connected to an additional component in the form of polejaws 12, 13, which ensure the necessary stability of the magnetic coreand serve as carriers for a further component in the form of a windingbody 14 (FIGS. 2 and 3). The relative alignment of the pole jaws 12, 13to the sheet stack 8 is appropriately carried out in that the pole jaws12, 13 are provided with holes 15, and are thrust with these on the endsof the rods 9 projecting out of the sheet stack 8, and then accommodatethese ends in themselves. Although the pole jaws can also consist ofiron, they are preferably made from aluminium in order to reduce weight.

The winding body 14 substantially consists of a frame made frominsulating material, e.g. plastic, which in the embodiment surrounds asubstantially cuboid cavity 16, whose dimensions of height, length andwidth substantially correspond to the external dimensions of the sheetstack 8 inclusive of the pole jaws 12 and 13. Moreover the winding body14 is provided on its upper and lower end with a respective outwardlyprojecting surrounding assembly flange 17, so that a surroundingaccommodation space 18 results for a winding 19 (FIG. 4) between the twoassembly flanges 17.

For correct positioning of the winding body 14 relative to the sheetstack 8, the pole jaws 12, 13 are provided on their outer end faces withguide grooves 20, which are disposed vertically to the rods 9 and to themagnet pole surface 10. Correspondingly, the winding body 14 has on twoopposite sides inwardly projecting guide ribs 21, which, when thewinding body 14 is set on the sheet stack 8 from above or below, enterthe guide grooves 20 and then enable a displacement of the winding body14 relative to the magnet pole surface 10 into a desired position (FIG.3), which is appropriately established by a stop means not shown infurther detail.

As is in particular seen from FIG. 4, the winding body 14, after itspositioning on the sheet stack 8, is provided with the winding 19, whichis formed from alternatively succeeding layers of a conductor 23 and ofan insulator 24, and comes to lie between the assembly flanges 17. Theconductor 23 consists for example of an endless aluminium strip unwoundfrom a supply coil 25, while the insulator 24 for example is a strip ofa conventional insulating film unwound from a supply coil 26. Unwindingof the conductor 23 and of the insulator 24 from the supply coils 25,26, or their winding onto the winding body 14, is effected in a knownway in the direction of the arrows entered in FIG. 4. Naturally it wouldalso be alternatively possible to apply the winding 22 onto the windingbody 14 before the latter is mounted on the sheet stack 8, or thewinding, here shown as a layer winding, can be subdivided into aplurality of panels to be connected together.

In the assembly described in FIGS. 1 to 3 of a magnet core, theindividual plates 1 loosely threaded onto the rods 9, are held inposition only by the rods 9 and the winding body 14, the winding body 14abutting on the lateral edges 5, 6 of the sheets 1 and on the forward orrear sides of the pole jaws 12, 13. In contrast, the winding 19 is heldin position on the magnet core by the assembly flange 17. Thus thesheets 1 are simultaneously pressed against one another via the polejaws 12, 13 with a pre-selected pressure, so that they abut closely onone another. In order to connect all these parts securely, the assemblysubstantially visible from FIG. 4 is inserted into a mold or a shapingtool 28 (FIGS. 5 to 7); in the embodiment what is involved is a tool 28with two tool halves 29 and 30, which are provided similarly to aninjection moulding tool on opposite sides with apertures 31, 32, whichin the closed condition of the tool 28 (FIG. 7) form a cavity or hollowmold space, whose dimensions are only slightly larger than the outerdimensions of the finished wound magnet pole.

For correct positioning of the magnet pole in the cavity, there serve onthe one hand for example the lower assembly flanges 17, and on the otherhand if required additional positioning means 33. In the embodimentthese consist of rods, which project into holes 34 (FIG. 2), which areformed in the pole jaws 12, 13 additionally to the holes 16 and atpoints which remain accessible beneath the winding body 14 in theassembled condition, as in particular FIG. 6 shows. The positioningmeans 33 are for example mounted in the side jaws of the tool half 30and upon closing of the tool 28 are moved automatically into the holes34. Further positioning means not shown may be disposed in the base ofthe tool half 30. In this way it is possible to align the sheet stack 8and the winding body 14 relative to one another in the tool.

One of the tool halves 29, 30 is provided according to FIG. 7 with aninlet opening extending as far as the cavity, to which is connected theoutlet of a line 37 provided with a control valve 6, and which inaddition has two inlets 40 and 41 each connected to a metering pump 38and 39. Preceding the metering pumps 38, 39 in each case is a respectivemixing container 42, 43 and following them is a mixer 44 incorporated inthe line 37. These devices serve the purpose of preparing a hardenablemixture, in particular a casting resin mixture, and after closing thetool 28, of introducing it into the cavity. In this way, in one singleworking step, a plurality of objects are achieved. On the one hand theloosely stacked sheets 1 of the sheet stack 8, by means of insertion ofthe mixture, are provided with the adhesive layers necessary betweenthem, and simultaneously with the use of an adhesive, they are connectedtogether to form a solid packet. On the other hand this packet isconnected with the assembly 45 forming with the other components of thefinished magnet pole (FIG. 8), to form a solid constructive unit, whichsimultaneously is covered as an entire unit and in particular at the cutedge of the sheets 1, with an anti-corrosion layer, which is indicatedschematically in FIG. 6 by a line 46. The pre-selectable thickness ofthis layer substantially depends on the spacing between the variouscomponents of the assembly after insertion into the tool from oneanother, and from the wall portions defining the cavity, and can forexample come to up to 10 mm, preferably 2 to 3 mm. Moreover, theassembly 45, due to the complete coverage with the hardenable mixture,receives its final mechanical electromagnetic and geometric properties,the special design of the tool 28 depending on the individual case, andthe apertures 31, 32 forming the mold hollow, contributing to this.

The mixture to be used is preferably a hardenable (Duroplastic) castingresin mix based on epoxy or polycyloolefine and consists for example oftwo components, namely for example a casting resin prepared in themixing container 42 and if necessary provided with an additive, e.g. anepoxy resin or an epoxy resin mixture, and a hardener prepared in themixing container 43, e.g. an epoxy hardener. The two components aremetered in a preselected ratio by means of the metering pumps 38, 39,introduced into the mixer 44, intimately mixed together therein and thenfrom that point introduced via the line 37 and the control valve 36 intothe cavity. Thus supply of the casting resin mixture is effected at apressure of e.g. 1-3 bar, in order in particular to wet through orimpregnate the sheet stack 8 in such a way that all the plates arecovered on all sides by a thin casting resin layer.

After the cavity is filled, the casting resin mixture, preferably withheating of the entire tool 28, is left to harden, until removal from themold can take place and the finished assembly 45 can be removed from thetool 28. Alternatively, the tool 28 may also be heated beforeintroduction of the casting resin mass. Moreover, it is best only toharden the casting resin mass in the tool 28 and then to subject thefinished assemblies 45 to a heat treatment, in order for example toterminate the hardening procedure and/or to expel slowly-evaporatingcomponents. In addition, a cleaning stage could be added.

In an embodiment of the invention felt to be best until now, the castingresin mixture is introduced after the pressure-gelating procedure intothe cavities between the plates 1 and the other components of theassembly 45, or between these and the walls of the mold hollow. Thepressure-gelating process is particularly advantageous, as the shrinkageoccurring during hardening is compensated for in this way. In thismethod, which is also termed a reaction resin injection molding (e.g.Kunststoff-Lexikon, Hrg. Dr.-Ing. K. Stoeckhart and Prof. Dr.-Ing. W.Woebcken, Carl Hanser Verlag, München, BRD, 8th edition, 1992), bothreaction resin masses with a long pot time and also highly-reactiveresin masses can be used, which are automatically mixed and metered withthe aid of the mix container 42, 43 only briefly before injection intothe tool 28, in an automatic manner. Thus the two inlets 40, 41 shown inFIG. 7 can also open into a pressure container, from which the preparedreaction resin mixture is then expressed into the line 37 by means ofcompressed air.

Numerous mixtures, particularly those which are thermally hardenable,are suitable for producing the assembly 45.

Preferred hardenable mixtures are epoxy resin/hardener mixtures andmixtures of a tensioned cycloolefine and a catalyst for the ring-openingmetathesis polymerisation.

Suitable as epoxy resins, which can be used according to the inventionare all types of epoxy resins, for example those which contain groups ofthe formula

directly bonded to oxygen, nitrogen or sulphur atoms, in which either R′and R″ each contain one hydrogen atom, in which case R″ means a hydrogenatom or a methyl group, or R′ and R″ together represent —CH2CH2 of—CH2CH2CH2-, in which case R″ means a hydrogen atom. As examples of suchresins there should be mentioned polyglycidylesters andpoly(β-methylglycidyl)esters, which can be obtained by conversion of acompound containing two or more carboxylic acid groups per molecule withepichloryhdrin, glycerine dichlorhydrin or β-methylepichloryhydrin inthe presence of alkali. Such polyglycidyl esters can be derived fromaliphatic polycarboxylic acids, e.g. oxalic acid, succinic acid,glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid,sebacic acid or dimerized or trimerized linolaic acid, from acycloaliphatic polycarboxylic acids such as tetrahydrophthalic acid,4-methyltetrahydrophthalic acid, hexahydrophthalic acid and4-methylhexahydrophthalic acid, and from aromatic polycarboxylic acids,such as phthalic acid, isophthalic acid and terephthalic acid.

Further examples are polyglycidyl ethers and poly(β-methylglycidyl)ethers, which are obtainable by conversion of a compound containing atleast two free alcoholic and/or phenolic hydroxyl groups per moleculewith the corresponding epichlorhydrin under alkaline conditions, or alsoin the presence of an acidic catalyst with subsequent alkali treatment.

These ethers can be produced with poly-(epichlorhydrin) from acyclicalcohols, such as ethylene glycol, diethylene glycol and higherpoly-(oxyethylene)-glycols, propane-1,2-diol undpoly-(oxypropylene)-glycols, propane-1,3-diol, butane-1,4-diol,poly-(oxytetramethylene)-glycols, pentane-1,5-diol, hexane-1,6-diol,hexane-2,4,6-triol, glycerine, 1,1,1-trimethylolpropane, pentaerythriteund sorbite, from cycloaliphatic alcohols, such as resorcite, chinite,bis-(4-hydroxycyclohexyl)-methane, 2,2-bis-(4-hydroxycyclohexyl)propaneand 1,1-bis-(hydroxymethyl)-cyclohexene-3, and from alcohols witharomatic cores, such as N,N-bis-(2-hydroxyethyl)-aniline andp,p′-bis-(2-hydroxyethylamino)-diphenylmethane. They can also beproduced from single-core phenols, such as resorcin und hydroquinone,and multicore phenols such as bis-(4-hydroxyphenyl)-methane,4-4dihydroxydiphenyl, bis-(4hydroxyphenyl)-sulfone,1,1,2,2-tetrakis-(4hydroxyphenyl)ethane, 2,2-bis-(4-hydroxyphenyl)propane (bisphenol A) and 2,2-bis-(3,5-dibromo-4hydroxyphenyl)-propane.

Further suitable hydroxy compounds for producing polyglycidyl ethers andpoly(β-methylglycidyl) ethers, are the novolacks obtainable bycondensation of aldeyhdes, such as formaldehyde, acetaldehyde, chloraland furfural and phenoline, such for example as phenol, o-cresol,m-cresol, p-cresol, 3,5-dimethylphenol, 4-chlorphenol and4-tert.-butylphenol.

Poly-(N-glycidyl)-compounds can be obtained for example bydehydrochlorination of the conversion products of epichloryhdrin with atleast two amines containing amino hydrogen atoms, such as such asaniline, n-butylamine, bis-(4-aminophenyl methane, andbis-(4-methylaminophenyl)-methane. Further suitablepoly-(n-glycidyl)compounds are triglycidylisocyanurate andn,n′-diglycidyl derivates of cyclic alkylene ureas, such asethylene-urea and 1,3-propylene-urea, and hydantoines, such for exampleas 5,5-dimethylhydantoine.

Poly-(S-glycidyl)-compounds are for example the Di-S-glycidylderivatives of dithiolene, such as ethane-1,2-dithiol andBis-(4-mercaptomethylphenyl)-ether.

Examples of epoxy resins with groups of the formula

wherein R′ and R″ together mean a —CH2CH2- or a —CH2-CH2-CH2-CH2-group,are bis-(2,3-epoxycyclopentyl)-ether, 2,3-epoxycyclopentylglycidylether,1,2-bis-(2,3-epoxycyclopentyloxy)-ethane and3′,4′-epoxycyclohexylrnethyl-3′,4′-epoxycyclohexane-carboxylate.

Also considered are epoxy resins, in which the glycidyl groups orβ-methylglycidyl groups are bonded to heteroatoms of various types, e.g.the N,N,O-triglycidyl derivate of 4-aminophenol, theglycidylether/glycidylester of salicylic acid or p-hydroxybenzoic acid,N-glycidyl-N′-(2-glycidyloxypropyl)-5,5dimethylhydantoine and2-glycidyloxy-1,3-bis-(5,5-dimethyl-1-glycidylhydantoinyl-3)-propane.

If required, epoxy resin mixtures can be used.

Preferably, diglycidylethers of bisphenols are used. Examples includebisphenol A-diglycidyl ether, bisphenol F-diglycidyl ether and bisphenolS-diglycidyl ether. Bisphenol A-diglycidyl ether is particularlypreferred.

Quite particularly preferred are liquid and low-viscosity epoxy resins.Appropriately the viscosity at 25° C. does not exceed a value of 20′000mPas.

In a method according to the invention, all the known epoxy resinhardeners can in theory be used.

Preferably a carboxylic acid or a carboxylic acid anhydride is used asan epoxy hardener.

Suitable carboxlic acids include

aliphatic dicarboxylic acids, such as oxalic acid, malic acid, succinicacid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaicacid, sebacic acid, 3, 6, 9-trioxaundecandic acid, or dimerized ortrimerized linoleic acid;

cycloaliphatic polycarboxylic acids, such as tetrahydrophthalic acid,4-methyltetrahydrophthalic acid, hexahydrophthalic acid and4-methylhexahydrophthalic acid; aromatic dicarboxylic acids, such asphthalic acid, isophthalic acid, terephthalic acid or naphthalic acid;

or diester-dicarbooxylic acids, which are obtainable for example byconversion of glycols, e.g. polypropylene glycol with two equivalentsdicarboxylic acid anhydride, such e.g. as tetrahydrophthalic acidanhydride.

Preferably liquid or easily-melting dicarboxylic acid anhydrides areused as epoxy resin hardeners.

Particularly preferred anhydride hardeners are methylnadicanhydride,tetrahydrophthalic acid anhydride and methyltetrahydrophthalic acidanhydride, methylnadicanhydride and methyltetrahydrophthalic acidanhydride being preferably used as an isomer mixture.

If required the anhydride hardener can be used in combination with areaction accelerator conventional for anhydride hardeners. As reactionaccelerators tertiary amines, carboxylic acid salts, metal chelates ororganophosphenes, for example, are suitable. Preferred accelerators arethe tertiary amines, such for example as N, N-dimethylbenzalamine, orsubstituted imidazoles.

In a further preferred embodiment of the invention, there is used as ahardenable mixture a mixture of a tensioned cycloolefine and a catalystfor the ring-opening metathesis polymerisation.

A particular advantage of the method described for manufacturing theassembly 45 resides in the fact that the process steps of impregnationof the loosely layered sheet stack 8, surrounding of the othercomponents and of the entire assembly 45 with an anti-corrosion layer 46(FIG. 6) and the secure connection of all parts together can be effectedin one single working step, without the necessity for additionalmechanical connecting means. Thus the procedures of loading andunloading the tool 28, opening and closing the tool 28 and filling ofthe remaining cavities within the hollow mold may be to a large extentautomated.

If in addition hardenable mixtures with electrically insulatingproperties are used, which applies to the above-named materials, thenthere results the further advantage that the sheets 1 are surrounded inthe single named working step with an electrically insulating layer, sothat in theory also entirely untreated magnetic steel sheets having noinsulating layers, can be used as initial materials.

A further outstanding advantage of the invention in this case resides inthe fact that the individual sheets 1 of the sheet stack 8 can beinserted in an in fact totally untreated but however stacked and denselypacked condition into the tool 28. Due to the natural surface roughnessin the area of their wide sides 7, there remain between the sheets 1,even in the stacked, densely packed condition a sufficiently largenumber and size of cavities, which fill with this mixture upon itspenetration into the tool 28, which then, in the hardened condition,provides the necessary insulation between the individual sheets 1without the formation of disruptive bubbles of the like. This effect canbe further improved and optimized in that, before or during injection ofthe mixture, the cavity is at least partly evacuated, in order toproduce a slight reduction in pressure of e.g. 2 to 10 millibars, ifnecessary to be determined by tests, and thus to suction the mixtureadditionally into the cavity, so that simultaneously the necessity isremoved of expelling the air still located in the cavity with the aid ofthe mixture.

Finally a further advantage is that the external shape of the assembly45 can be selected substantially independently of the shape of theindividual sheets 1 produced by stamping, and of the winding 19 laidaround it. In particular, by means of corresponding formation of themold hollow, it can be assured that the external anti-corrosion layer issufficiently thick and environmentally resistant, whilst simultaneouslyby means of the stacking of the sheets 1 and the pressure used to clampthem, the required thin adhesive and if necessary insulating layers canbe produced between the individual sheets 1.

The embodiment according to FIGS. 1 to 8 may be modified and/orsupplemented in many ways.

Particularly, the undersides 4 (FIG. 1) of the sheets 1 of the entiresheet stack and/or the undersides of the pole jaws 12, 13 can be keptfree of mixture. For this purpose for example the cavity of the tool 28is so designed that the undersides, after location of the variouscomponents in the tool 28, abut directly on corresponding wall portions.As the undersides of the sheet stacks and/or of the pole jaws 12, 13 ina complete magnet, usually consisting of a plurality of such magnetpoles, are magnetically connected together by means of ferromagneticpole backs located beneath the windings 19, it is ensured in this waythat in the boundary surfaces between the magnet poles and the magnetback no magnetically disruptive slots formed by included mixture arise.

FIGS. 9 to 14 show the manufacture of a sheet stack 51 for the stator ofan electrical alternating current motor. Similarly to FIGS. 1 to 8, thesheet stack 51 includes a plurality of plates or lamellae 52, which areshown in the upper portion of FIG. 9 in the exploded condition and inthe lower portion of FIG. 9 in the ready stacked condition abuttingparallel and flush on one another. The sheets 52 are obtained bystamping out from a raw ferromagnetic sheet metal strip or the likewhich has no adhesive layer. The sheets 52 in the embodiment haveidentical dimensions and, as can be seen from the plan view in FIG. 10,have a circular form. On their inner circumference, the sheets 52 areprovided with U-shaped cut-outs 53, which in the stacked condition arealigned towards one another and form continuous grooves. In a known way,groove sleeves 54 are pressed into these grooves, said groove sleevesaccording to FIG. 9 extending over the entire height of the sheet stack51 and enabling the formation of the stack in a simple way.

The groove sleeves 54 serve to accommodate windings 55 (FIG. 9) thecenter lines of which have a substantially flat-oval configuration, ascan be seen from the front view or plan view according to FIGS. 9 and10, for a winding 55 which is not yet mounted. These correspondinglyprepared windings 55, in dependence on the type of winding provided foran individual case, are pressed with their long sides into groovesleeves 54 (FIG. 10), which are spaced apart by two or a multiple oftimes, in FIG. 10 by three times the groove division from one another,while their short sides form the winding heads. Therefore, in theassembled condition, the winding 55 adopts the position indicated by thebroken line 55 a (see also FIG. 11). The groove sleeves 54 appropriatelyconsist of paper, cardboard or an insulating plastic, so that thewindings 55 are sufficiently insulated from the plates 52, even if theselatter have no insulating layer or have lost it due to the stampingprocedure. In order axially to secure the groove sleeves 54 in the sheetstack 51, respective groove sleeve collars 56 (FIG. 11) can be used,which are clipped onto the upper or lower ends of the groove sleeves 54,or may also be integrated in the groove sleeves 54 as a fold.

After all the windings 55 have been inserted into the associated groovesleeves 54 and have been electrically interconnected in the necessaryway (FIG. 11), the loosely pre-mounted assembly is introduced, similarlyto the assembly according to FIG. 4, into a tool 59 (FIGS. 12, 13) whichin the embodiment has two tool halves 60, 61, which are provided onsides facing one another with apertures 62, 63, which in the closedcondition of the tool 59 form a mold hollow or cavity, the dimensions ofwhich are slightly greater than the external dimensions of the insertedassembly. The assembly may be positioned in the tool similarly to FIG. 6with the aid of spacers or other positioning aids not shown, whichpreferably engage on the assembly at points where no surrounding with ahardenable mixture is necessary.

After the tool 59 is closed in the direction of the arrows appearing inFIG. 12, a hardenable mixture is introduced into the cavity, for whichpurpose the tool 59, similarly to FIG. 7, is provided with an inletopening extending as far as the cavity, and which is connected by meansof a line 64 (FIG. 14) to a control valve 65 and via metering pumps 66,67 to mixing containers 68, 69, which contain a reaction resin or ahardener or the like, in order to prepare the mixture therefrom. Thereaction resin and hardener ingredients metered by the metering pumps66, 67 are mixed in a mixer 70. The method steps of introduction of themixture into the cavity, of hardening or hardening out of the mixture,of heat treatment and if necessary cleaning are similar to theembodiment according to FIGS. 1 to 8 and therefore need not be describedagain. The same applies to the usable mixtures, particularly castingresin mixtures, whose preparation, the preferred injection of themixture at a pressure of e.g. 1 to 3 bar, the preferable additionalevacuation of the cavity and the preferred use of the pressure-gelatingmethod.

After removal from the mold, the finished assembly 71 visible in FIG. 14is obtained in the form of a stator. This assembly 71 is provided allround with an anti-corrosion and if necessary insulating layer 72, thethickness of which corresponds to the spacing between the variouscomponents and the walls of the associated tool halves 60, 61 in theclosed condition of the tool 59, and can be correspondinglypre-selected.

The advantages attained in manufacturing the assembly 71 according tothe method described are similar to those explained in conjunction withthe assembly 45. Thus the external shape of the finished assembly 71 canbe selected to a large extent independently on the stamped shape of theindividual sheets 52, so that as required the final electrical,magnetic, mechanical and/or geometric properties of the sheet stacks orof the assembly 71 are at least partly obtained only by the treatment ofall components with the hardenable mixture in a tool. This appliesparticularly with respect to the application of the layers between theindividual sheets, the external anti-corrosion layer, the permanentinterconnection of the various parts and the final external shape of thesurrounded sheet stacks, assemblies or parts thereof. A particularadvantage in addition is that additional connecting means such forexample as screws, rivets, adhesives or the like are required neitherfor positioning nor for connecting the individual parts, and themechanical strength and environmental resistance can be established bythe thickness of the external covering with the hardenable mixture.

As shown in particular by FIG. 11, it may also be appropriate to coverthe sheet stacks or assemblies inserted into the tool at specificpoints, e.g. on their outer sides, with a spacer member 73 produced froma porous material, consisting e.g. of a woven mat produced from plasticfibres or the like, which holds the sheet stack 51 or the like at adesired spacing from the walls of the mold hollow. Such elements or matsare fully impregnated with the mixture during the injection procedure,so that during hardening a stable, strong plastic resin layer results,which forms a mechanically strong external wall on the finished assembly71 and increases its mechanical strength.

In order to improve the electrical properties (dielectric constant, lossfactor) silanes, e.g. the compounds offered by the Company OsiSpecialties under the tradename Silquest Silane maybe added to thehardenable mixtures. Suitable silanes are for exampleoctyltriethoxysilane, methyltriethoxysilane and vinyltriethoxysilane.

In addition, the hardenable mixtures can contain fillers such forexample as metal powder, wood powder, glass powder, glass pearls orsemi-metal and metal oxides. Preferred fillers are Wollastonite, Al203and SiO2, quartz powder of the various SiO2 modifications beingparticularly preferred.

In addition to the additives mentioned, further additives such asanti-oxidising agents, light-protective agents, plasticisers, pigments,dye stuffs, thixotropic agents, viscosity improvers, de-foamers,anti-static agents, lubricants and mold release agents can be containedin the hardenable mixtures.

Moreover, the hardenable mixtures may be produced according to knownmethods, conventionally with the aid of known mixing units (stirrers,kneaders, rollers, mills, dry mixers or thin-layer de-gassing mixers).The various methods for producing mixtures are known to the personskilled in the art and are for example described in Becker/Braun is“Kunstoff-Handbuch, vol. 10, Duroplaste”, Carl Hanser Verlag 1988, pages515 ff and 825 ff.

If it is desired to stack the individual sheets 1, 61 in a way otherthan that explained above, they can be fixed with appropriate auxiliarymeans, e.g. spacers, on the ends in such a way that the spacings betweenthe individual sheets are approximately equal. In this case it isirrelevant that the spaces between all the plates are exactly identical.There need only be sufficient room for entry of the insulating resincompound into the inter-spaces between the individual plates 1, 61. Thespacing between the plates 1 in this way can be adjusted for examplefrom 1 μm to 100 μm, preferably to 2 μm to 5 μm.

The metal plates usable in the method according to the invention arepreferably steel plates, although other ferromagnetic materials can alsobe used.

The invention is not restricted to the embodiments described by way ofexample, which may be varied in many ways. This applies in particularwith respect to the assemblies having ferromagnetic sheet stacks andwhich can be manufactured according to the method described. Accordingto the method described, sheet stacks of all types for all types ofapparatus may be manufactured, which have a magnetic circuit, which forelectromagnetic purposes require a sheet stack assembled from individualplates. Independently thereof, the sheet stacks may be individuallymanufactured according to the method described, and may be subsequentlycombined in a conventional method of construction with other componentsin order to form assemblies. Thus it is self-evident that the sheetstacks and/or assemblies described can be provided also with othercomponents not described in more detail, e.g. with externally-leadingelectrical or mechanical connections, which are likewise fixed and/orformed by the surrounding hardenable mixture. Finally the inventioncomprises also the sheet stacks and assemblies manufactured according tothe described method, the individual features being also applicable incombinations other than those described and illustrated in the drawing.

What is claimed is:
 1. A method of manufacturing a finished sheet stack,consisting of ferromagnetic material, for electromagnetic assemblies,said method comprising the steps of: providing a plurality of rawmagnetic steel sheets; stacking said sheets for providing a sheet stack;positioning said stack in a cavity defined by wall portions of a shapingtool; and then providing said finished sheet stack by means of apressure-gelation method said pressure-gelation method comprising thesteps of providing a liquid, thermally hardenable mixture whichcomprises a duroplastic epoxy resin component and a hardener component;introducing said mixture under pressure into said cavity such that saidmixture is introduced into cavities between said sheets so as to connectthem with one another as well as surrounds said sheets and said sheetstack as a whole on preselected sides; hardening or hardening out saidmixture at least as long until removal of said sheets stack from saidshaping tool can take place; and heating said shaping tool at leastduring hardening or hardening onto said mixture; whereby in one singleworking step, both said sheets are connected together and said sheetsand said sheet stack are surrounded on said preselected sides with ananti-corrosion layer having a thickness which is selected by a spacingbetween said sheet stack and said wall portions of said shaping tool. 2.The method as defined in claim 1, wherein said raw magnetic steel sheetsare not pre-treated and the hardenable mixture has a composition withelectrical insulating properties so that a mutual electrical insulationis formed between said sheets.
 3. The method as defined in claim 1,wherein said sheets and said sheet stack are completely surrounded withsaid anti-corrosion layer.
 4. The method according to claim 1, whereinsaid cavity is at least partly evacuated before or during introductionof said mixture into said cavity.
 5. A method as defined in claim 1,further using at least one section of the sheet stack for mounting apositioning member during introduction of the sheet stack into theshaping tool.
 6. A method as defined in claim 1, further using a spacermember made of a porous material as a positioning member duringintroduction of the sheet stack into the shaping tool.
 7. A method ofmanufacturing an electromagnetic assembly including at least one sheetstack, consisting of ferromagnetic material, and an additionalcomponent, said method comprising the steps of: providing a plurality ofraw magnetic steel sheets; stacking said sheets for providing a sheetstack, forming said assembly from said stack and said component;positioning said assembly in a cavity defined by wall portions of ashaping tool and then providing said finished assembly by means of apressure-gelation method, said pressure-gelation method comprising thesteps of providing a liquid, thermally hardenable mixture whichcomprises a duroplastic epoxy resin component and a hardener component;introducing said mixture under pressure into said cavity such that saidmixture is introduced into cavities between said sheets so as to connectthem with one another as well as surrounds said sheets, said sheet stackand said assembly as a whole on preselected sides; hardening orhardening out said mixture at least as long until removal of saidassembly from said shaping tool can take place; and heating said shapingtool at least during hardening or hardening onto said mixture; wherebyin one single working step, said sheets are connected together, saidstack is connected with said component and said assembly is surroundedon said preselected sides with an anti-corrosion layer having athickness which is selected by a spacing between said sheet stack, saidcomponent and said wall portions of said spacing tool.
 8. The method asdefined in claim 7, wherein said raw magnetic steel sheets are notpre-treated and the hardenable mixture has a composition with electricalinsulating properties so that a mutual electrical insulation is formedbetween said sheets.
 9. The method according to claim 7, wherein saidsheets and said sheet stack are completely surrounded with saidanti-corrosion layer.
 10. The method according to claim 7, wherein saidcavity is at least partly evacuated before or during introduction ofsaid mixture into said cavity.
 11. A method as defined in claim 7,further using at least one section of the sheet stack for mounting apositioning member during introduction of the sheet stack into theshaping tool.
 12. A method as defined in claim 7, further using a spacermember made of a porous material as a positioning member duringintroduction of the sheet stack into the shaping tool.